The present invention relates to pneumatic service circuit for circular knitting machine service devices.
As is known, circular knitting machines have long used numerous pneumatic actuators in order to actuate the various service devices required for the operation of the machine, such as for example thread guides, movable cams for actuating the needles or sub-needles, extractors for oscillating selectors, selection devices, thread cutting and clamping units, etc.
Actuation of the various devices by means of pneumatic actuators is increasingly used by manufacturers of these types of machines, since it extremely simplifies the connection of the various service devices to an electronic central control unit which is capable of actuating the various devices, according to a preset program, simply by actuating electric valves arranged along the supply ducts of the pneumatic actuators.
In currently commercially available machines, the pneumatic service circuit is generally constituted by a control unit which combines all the electric valves actuated by the central unit and from which the supply ducts of the various pneumatic actuators, constituted by flexible tubes, extend.
Although the control unit is arranged proximate to the needle cylinder of the machine, the supply ducts of the various pneumatic actuators to be actuated are relatively long and constitute a bulk which must be taken into account during the design of the machine in order to avoid interference between the various ducts and the other elements required for the operation of the machine.
The length of the supply ducts, which generally have a reduced passage section, furthermore causes load losses which compulsorily require an increase in the supply pressure, which in turn necessitates the employment of valves which are oversized with respect to the pressure which is actually necessary in order to activate the pneumatic actuators.
With the pneumatic circuits which are currently used, one also observes problems during maintenance, since it is difficult to operate around the needle cylinder due to the presence of the pneumatic ducts which reach the various actuators, as well as high assembly costs due to the considerable number of pneumatic ducts and related couplings.